docs: def get_diff_idxs(array, rtol, atol):
      """
      Given an array with (C, N, L) values, being the first the reference value,
      compute the relative differences and discard the one below the tolerance.
      :returns: indices where there are sensible differences.
      """
      C, N, L = array.shape
      diff_idxs = set()  # indices of the sites with differences
      for c in range(1, C):
          for n in range(N):
              if not numpy.allclose(array[c, n], array[0, n], rtol, atol):
                  diff_idxs.add(n)
      return numpy.fromiter(diff_idxs, int)